The mechanism behind "check-all" is recording params of add_lit_testsuite()
calls in global variables LLVM_LIT_*, and then creating an extra suite with
their union at the end.
This avoids composing the check-* targets directly, which doesn't work well.
We generalize this by allowing multiple families of variables LLVM_{name}_LIT_*:
umbrella_lit_testsuite_begin(check-foo)
... test suites here will be added to LLVM_FOO_LIT_* variables ...
umbrella_lit_testsuite_end(check-foo)
(This also moves some implementation muck out of {llvm,clang}/CMakeLists.txt
This patch also changes check-clang-tools to use be an umbrella test target,
which means the clangd and clang-pseudo tests are included in it, along with the
the other testsuites that already are (like check-clang-extra-clang-tidy).
Differential Revision: https://reviews.llvm.org/D121838
7cc8377f2c